1 Strain: Use when an attack targeting you is declared to apply +1block to your defense results. You may convert 1 or more block results to evade results.

Does Jyn have to spend the strain to be allowed to convert block or is the strain just for the +1?

Does Jyn have to spend the strain to be allowed to convert block?

Yes she needs to suffer the Strain. If you could use that without suffering the Strain, it would be sectioned off on the card, like the 3 effects from "Sumggler's Luck"